Size as a determinant of robustness: Exploring sexual dimorphism in the size and shape of the snapping and cutting claws in Alpheus (caridea: Alpheidae)

Abstract

This study investigates the role of static allometry in modulating sexual shape dimorphism in the snapping and cutting claws of Alpheus species. We hypothesize that the static allometry in adulthood can promote an exaggeration of existing sexual dimorphism in the snapping and cutting claws of Alpheus. Sexually mature pairs from three species (Alpheus angulosus, Alpheus carlae, and Alpheus nuttingi) were analyzed using geometric morphometric techniques. The increase in size claw enhances the robustness of both snapping and cutting claws. Since males carry larger weapons compared to females, the static allometry provides more robustness in their weapons. These findings support our hypothesis. Due to the effect of static allometry, male weapons exhibit a more robust pollex, while female weapons exhibit a more robust palm in the snapping claw. Sexual shape dimorphism is less pronounced in the cutting claw, although males display larger and more robust claws compared to females. Static allometry amplifies the sexual differences in Alpheus weapons, emphasizing the role of sexual selection in the evolution of claw morphology. The results suggest that sexual selection favors larger, more robust claws in males, thus enhancing their effectiveness in agonistic contests.